K.P.
I think that you can explain how babies are made terms that a 4 yr old can understand. I haven't read any books on the subject to my kids, but when they asked I told them that first they have to be MARRIED to have babies. In my opinion, drilling that into their little heads early on is so important. In today's world there are too many young people who are way too casual about sex, and just give their bodies to the next "hook up" and don't think of the consequences. I haven't had to explain in detail what happens yet, but both of my kids know that mommy and daddy created them and that they had to stay in mommy's tummy until they were ready to be born. It's all about explaining it in terms they can understand. Pictures are helpful. Both of my kids have seen pictures of when I was pregnant with them, and they know that they were in my tummy then. They have also seen pictures of when they were born (the ones when they were being weighed). I have a 6 yr old boy and a 4 yr old girl, and when they ask a question, I just give them enough info to satisfy their curiosity. I don't think they need the whole "story" all at once. But, contrary to what others have said, with the way our young people view sex, it is not too early to start telling your kids about sex. Here in Idaho, a few months back, a 9 yr old girl gave birth. Not that she was a willing participant in having sex, but her little 9 yr old body was capable of bearing a child. So I think that the earlier you explain that sex is one way a HUSBAND and WIFE show each other that they love each other, the better chance you have that your kids will make good decisions in that department as they get older. You will definitely have several opportunities over the years to teach your children the consequences of sex before marriage, and will be able to instill your values. It's better to talk about than not.